Shift lever keeps getting loose on transmission shaft...help!

In recent months, I've been plagued with the shift lever coming loose on the transmission selector shaft, on my old dirt bike,
making gear changes unreliable and sometimes impossible! I just had the engine re-built and I'd like to use it!

Re-tightening the bolt on the shift lever has only helped temporarily.
Recently, I tried using an application of Loctite on the shifter bolt and also between the shifter and transmission shaft,
which resolved the problem, but again only temporarily.

Desperate, I've even considered a spot weld to hold the shifter on the selector, but that's not feasible
as the selector shaft is steel and the shifter is aluminum.
Maybe a dose of epoxy steel filler, between the shifter and transmission shaft might do the trick....??

I went to the moto (not motorcycle) shop who has maintained my moto for years and am often surprised by his ingenuity.
He waved me off as well as the red loctite and steel epoxy cement I'd brought with me.
He cut the head off of a standard rocker type moto shifter as well as the head off of my shifter.
He TIG welded the moto shifter to my shifter lever...and all is now well with my dirt-bike!
Later, I will add some loctite to the shifter bolt...just in case.